Metallacyclic Pyridylidene Structures from Reactions of Terminal Pyridylidenes with Alkenes and Acetylene

Abstract

Iridiumpyridyle sind Schlüsselintermediate in den Titelreaktionen. Die thermische Eliminierung von Benzol aus Komplexen 1 (R=Me, Ph) erzeugt eine freie Koordinationsstelle, die für ungesättigte Kohlenwasserstoffe zugänglich ist. Der nachfolgende intramolekulare nucleophile Angriff durch das Pyridyl‐Stickstoffatom an die Alken‐ oder Vinylidengruppe führt zu iridacyclischen Pyridylidenstrukturen (siehe Schema).

CN Bond Formation by O2‐Mediated Dehydrogenative Coupling of Phenyl and NH‐pyridylidene Ligands on TpIrIII Complexes

“…[11] The IrÀC carbene bond length (1.998 (3) ) is similar to that found in related cyclic pyridylidenes. [3,7,12] An ORTEP structure of complex 4 b is shown in Figure 2, with the two aromatic rings in the newly formed ligand being, as expected, almost coplanar. To obtain mechanistic information on this reaction, additional experiments were carried out.…”

“…Nonetheless, following recent work by Lewis, Bergman, and Ellman, [4] we have now prepared the parent pyridylidene 2 a (R = H) [5] by alkaline hydrolysis of the new carbene derived from 2-(trimethylsilyl)pyridine. [6] Since it is also known that carbenes 2 b (R = Me) and 2 c (R = Ph) react with CO and unsaturated hydrocarbons (e.g., C 2 H 2 , C 2 H 4 , and C 3 H 6 ) through reversible generation [7] of unsaturated pyridyl intermediate A (Scheme 1), we regarded it as worthwhile to investigate the reactivity of carbenes 2 a-c towards oxygen.…”

“…The scrambling is best ascertained upon inspection of the 13 C{ 1 H} NMR spectrum of the resulting product (Figure 3), in which the effects of deuterium atoms on the chemical shift of a given adjacent CH aromatic resonance [17] allow for a semi-quantitative study of the exchange. [7] would allow for the generation of a phenyl-benzyne-pyridyl intermediate [Tp…”

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H, Me, Ph)

“…Because these preliminary reports included the X‐ray structures of complexes 4 c and 11 b (see ref. 7a), as well as those of complexes 19 b and 20 b (see ref. 7b), the structures of these compounds will not be discussed herein.…”

Metall‐Ligand‐Kooperation

“…Ein interessantes Beispiel für Metall‐Ligand‐Kooperation wurde von Carmona et al. in den 2‐Pyridyliden‐Ir III ‐Komplexen 196 a,b beobachtet (Schema ) 152–154. Die Koordination des Pyridyliden‐Liganden resultiert aus der Tautomerisierung des 2‐substituierten Pyridins, induziert durch das Metallzentrum.…”